This invention relates to a heat transfer image-receiving sheet, and more particularly to a heat transfer image-receiving sheet capable of producing an image which is excellent in color density, sharpness, fastness, and, in particular, light resistance.
Heretofore, a variety of heat transfer printing methods have been proposed. Among them, a typical one for producing a full-colored image is a method which employs a heat transfer printing sheet comprising a sublimable dye as a coloring agent which is retained in a substrate such as a polyester film, and a heat transfer image-receiving sheet receptive of the sublimable dye, comprising a dye-receiving layer provided on the substrate such as a sheet of paper or a plastic film.
In the above method, heat is applied to the heat transfer printing sheet by a thermal head of a printer, and a large number of dots in three or four colors are transferred to the heat transfer image-receiving sheet in an extremely short heat-application time. An original full-colored image can thus be reproduced in the heat transfer image-receiving sheet.
The image thus obtained is very sharp and clear because a dye is used as a coloring material. Therefore, the heat transfer printing method of this type can provide an excellent half-tone image with continuous gradation, comparable to an image obtained by offset printing or gravure printing. Further, the quality of the image is as high as that of a full-colored photo.
Not only the structure of the heat transfer printing sheet, but also that of the heat transfer image-receiving sheet in which an image is produced are quite important factors in this printing method.
Namely, the dye-receiving layer of the heat transfer image-receiving sheet needs to be highly receptive of the sublimable dye contained in the heat transfer printing sheet, and can firmly retain it.
In the case where the dye-receiving layer is formed from a resin having a high affinity for the sublimable dye, it can be well dyed with the dye. However, in this case, an image produced in the dye-receiving layer will be blurred during storage. In addition, the dye transferred to the dye-receiving layer cannot be firmly retained therein, so that it bleeds out of the dye-receiving layer and tends to stain articles which are brought into contact with the surface of the dye-receiving layer.
The above shortcomings can be eliminated if the dye-receiving layer is prepared from a resin which does not allow the dye transferred from the heat transfer printing sheet to easily migrate to the dye-receiving layer. However, when such a resin is employed, the dye-receiving layer cannot be well dyed with the dye, and cannot produce a sharp image with high density.